code: def exp(expr):
      return ast.PowExpr(base_expr=ast.NumVal(math.e), exp_expr=expr)
  
file_path: m2cgen/m2cgen/assemblers/fallback_expressions.py
imports: import math
  from m2cgen import ast
  from m2cgen.assemblers import utils
label_desc: Use image node_id 4 for calling a global function with example usage: exp(expr) and returns: ast